Foamable molding compositions containing chemical blowing agents are known. U.S. Pat. No. 3,888,801 discloses the chemical blowing agents which are suitable in the context of the present invention. Resins which are suitable in the present invention are also disclosed in that patent.
Polycarbonate compositions having an improved level of impact strength comprising an aromatic polycarbonate, glass fibers and a polyanhydride have been disclosed in U.S. Pat. No. 4,420,584. In U.S. Pat. No. 4,207,402, there was disclosed foamable composition comprising an addition polymer in combination with an interpolymer of an alkyl aromatic monomer and maleic anhydride and a particular foaming agent. The advantages were said to be associated with the attainment of shorter molding cycles.
The art is also noted to include U.S. Pat. No. 4,737,523 which disclosed a foamable molding composition containing a thermoplastic resin, a polyanhydride compound which contains at least one cyclic anhydride in its structure, a blowing agent and a nucleating agent. In U.S. Pat. No. 4,751,250 there was disclosed a process for producing a foamed article containing a chemical blowing agent and entailing the use of an anhydride. The chemical blowing agent disclosed in the later two patents is identical to the one entailed in the present invention.